The invention relates to a device for arc welding with consumable metal wire allowing an operator to set the wire speed and automatically select, depending on the setting of the wire speed, a type of metal transfer regime. The invention also relates to a process for welding at least one metal part the performance of which is improved and the implementation of which is made easier by virtue of the device according to the invention.
Processes for arc welding with consumable metal wire under a gas flow, also called metal inert gas (MIG) or metal active gas (MAG) welding, rely on the use of an electric arc drawn between the end of a consumable metal wire, serving as a consumable electrode, and the metal parts to be welded. The heat of the electric arc allows both the constituent metal of the parts to be welded and the constituent metal of the consumable wire to be melted, thereby generating a weld bath formed from the molten constituent metal of the parts to be welded and of the metal of the melted consumable wire transferred in the electric arc toward the weld bath.
An arc welding process is generally carried out with a welding torch positioned facing the metal parts to be welded. The torch holds at its end the terminal portion of the consumable metal wire. The welding torch is also equipped with a nozzle distributing a flow of shielding gas over the weld bath in order to protect it from the surrounding atmosphere.
The torch is electrically connected to an arc welding unit, conventionally comprising at least one source of shielding gas supplying the torch, a current generator supplying the consumable wire with electrical current and a wire feeder allowing the wire to be fed out of the torch in the direction of the weld bath at a controlled wire speed.
An arc welding unit generally comprises means for selecting welding parameters, especially arc voltage, wire speed, i.e. the speed at which the wire is fed, smooth or pulsed current, etc.
The selected welding parameters result in a given type of metal transfer regime. More precisely, these parameters determine the welding energy, which determines the shape of the end of the wire when it is melted by the flow of current, and the way in which the constituent metal of the molten wire is transferred to the weld bath, i.e. the transfer regime.
At the present time, electric current generators, such as inverter and/or chopper generators, are widely employed in MIG or MAG welding because they allow arc current to be precisely controlled. In particular, they offer the possibility of imposing on the current particular waveforms as a function of time. It is then possible to control the detachment of the drop at the end of the wire, in order to work in a transfer regime suitable for the welding process to be implemented, for example in order to minimize projections of molten metal.
Typically, welding devices are equipped with electric generators in which the welding parameters, especially the magnitude of the current, i.e. the welding current, arc voltage and wire speed are programmed to vary together, and as a function of the wire speed, according to a preset relationship called a synergy. In general, these synergies are established beforehand by the manufacturer and memorized in the welding units.
Customarily, before a welding operation begins the operator selects a synergy suitable for the desired welding process, this process being defined by the type of material to be welded, the type of consumable wire, the type of gas, the type of the assembly or joint, the welding position, the type of metal transfer regime, etc. Once the synergy has been selected, the operator sets the wire speed and optionally sets the arc length. The current generator then automatically sets the welding parameters and the welding operation begins.
However, this operating mode is not entirely satisfactory.
Specifically, the type of metal transfer is selected at the welding unit when the initial synergy is chosen.
However, it is frequently the case that an operator welding an assembly with a given type of transfer regime will want to increase the feed speed of the wire, i.e. the rate at which the wire is melted, so as to increase productivity or deposition rate.
As wire speed, current and arc voltage are balanced, an increase in the wire speed implies an increase in current, which inevitably causes, above a certain wire speed, a change of transfer regime. The operator may thus be led to select involuntarily a transfer regime that is unsuitable for the welding process being carried out, for example a spray regime or a regime that is too energetic for the thickness to be welded or unwieldy in the desired welding position.
The operator is then obliged to select at the welding unit another synergy allowing him to obtain satisfactory results with the new wire speed setting. The ensuing adjustment operations are tedious and require a plurality of successive adjustment sequences and trial welds to be carried out.